Without knowing how the database is structured and how the excel sheet
is laid out it's not possible to offer any specific advice.
Even if the Access database isn't on a web server, it still sounds as if
you want changes to the Access data to "flow through" to the Excel
worksheet. Normally this is reasonably simple. This article
http://support.microsoft.com/?id=247412 describes most of the available
approaches. (It's written from the perspective of Visual Basic but
virtually all of it applies to Access VBA; perhaps the most important
difference is that both the methods it describes that use ADO work
equally well with DAO. In the most recent versions of Access, however,
the "Transfer data to a worksheet by using ADO" approach no longer works
as described in the August 2005 version of the article; it should be
updated soon, so check the "Last Review" date.)
The main problem I see is that if there's a single "days off calendar"
workbook shared by many employees, and "very busy" means that for much
of the time at least one person has the workbook open, the database will
find the workbook "locked" when it tries to update it. This in turn will
mean that people opening the workbook won't be able to rely on it to
show them the latest data. This is definitely an Excel problem rather
than an Access one, so I stand by my advice that you should go to an
Excel forum.
Alternatively, dump the workbook and replace it with a "front end"
application draws live data from the database to build a similar view of
days off. This could be an Access database, a VB application, or a web
page.